Because terrorism educes such strong emotions, it has led to at least five myths. The first began in September 2001, when President George W. Bush announced that “we will rid the world of the evildoers” and that they hate us for our “our freedoms.” This sentiment embodies what Florida State University psychologist Roy F. Baumeister calls “the myth of pure evil,” which holds that perpetrators commit pointless violence for no rational reason.

This idea is busted through the scientific study of aggression, of which psychologists have identified four types that are employed toward a purposeful end (from the perpetrators' perspective): instrumental violence, such as plunder, conquest and the elimination of rivals; revenge, such as vendettas against adversaries or self-help justice; dominance and recognition, such as competition for status and women, particularly among young males; and ideology, such as religious beliefs or utopian creeds. Terrorists are motivated by a mixture of all four.

In a study of 52 cases of Islamist extremists who have targeted the U.S. for terrorism, for example, Ohio State University political scientist John Mueller concluded that their motives are often instrumental and revenge-oriented, a “boiling outrage at U.S. foreign policy—the wars in Iraq and Afghanistan, in particular, and the country's support for Israel in the Palestinian conflict.” Ideology in the form of religion “was a part of the consideration for most,” Mueller suggests, “but not because they wished to spread Sharia law or to establish caliphates (few of the culprits would be able to spell either word). Rather they wanted to protect their co-religionists against what was commonly seen to be a concentrated war on them in the Middle East by the U.S. government.”

As for dominance and recognition, University of Michigan anthropologist Scott Atran has demonstrated that suicide bombers (and their families) are showered with status and honor in this life and the promise of women in the next and that most “belong to loose, homegrown networks of family and friends who die not just for a cause but for each other.” Most terrorists are in their late teens or early 20s and “are especially prone to movements that promise a meaningful cause, camaraderie, adventure and glory,” he adds.

Busting a second fallacy—that terrorists are part of a vast global network of top-down centrally controlled conspiracies against the West—Atran shows that it is “a decentralized, self-organizing and constantly evolving complex of social networks.” A third flawed notion is that terrorists are diabolical geniuses, as when the 9/11 Commission report described them as “sophisticated, patient, disciplined, and lethal.” But according to Johns Hopkins University political scientist Max Abrahms, after the decapitation of the leadership of the top extremist organizations, “terrorists targeting the American homeland have been neither sophisticated nor masterminds, but incompetent fools.”

Examples abound: the 2001 airplane shoe bomber Richard Reid was unable to ignite the fuse because it was wet from rain; the 2009 underwear bomber Umar Farouk Abdulmutallab succeeded only in torching his junk; the 2010 Times Square bomber Faisal Shahzad managed merely to burn the inside of his Nissan Pathfinder; and the 2012 model airplane bomber Rezwan Ferdaus purchased faux C-4 explosives from fbi agents. Most recently, the 2013 Boston Marathon bombers appear to have been equipped with only one gun and had no exit strategy beyond hijacking a car low on gas that Dzhokhar Tsarnaev used to run over his brother, Tamerlan, followed by a failed suicide attempt inside a land-based boat.

A fourth fiction is that terrorism is deadly. Compared with the annual average of 13,700 homicides, however, deaths from terrorism are statistically invisible, with a total of 33 in the U.S. since 9/11.

Finally, a fifth figment about terrorism is that it works. In an analysis of 457 terrorist campaigns since 1968, George Mason University political scientist Audrey Cronin found that not one extremist group conquered a state and that a full 94 percent failed to gain even one of their strategic goals. Her 2009 book is entitled How Terrorism Ends (Princeton University Press). It ends swiftly (groups survive eight years on average) and badly (the death of its leaders).

We must be vigilant always, of course, but these myths point to the inexorable conclusion that terrorism is nothing like what its perpetrators wish it were.